Friel-Sturdy radiographic slide rule with case by the Unique Slide Rule Company, used to determine exposure times for medical X-rays. Friel-Sturdy radiographic slide rule with case, to determine exposure times for medical X-rays circa 1946
`Unique' 10-inch slide rule in cardboard case, with tables containing properties of materials on the back, c. 1940, made in England `Unique' 10-inch slide rule in cardboard case 1940